Dispatcher reported confusion and communications issues while working a flight that diverted due to the loss of the APU generator; which when combined with an engine IDG already on MEL required the Flight Crew to divert and land at the nearest suitable airport.

Narrative

Flight diversion occurred to ZZZ due to an enroute failure of the APU Generator. The #1 engine generator was initially on placard bringing the flight down to one single AC power source. No non-normal situation exists in the Flight Manual; but is trained that a single AC sources requires diversion to the nearest suitable airport. The Dispatcher contacted the Operations Manager immediately after the flight crew reported the event. I was notified of the event by calling the Dispatch to inquire about the flight status when [Software Program] alerted that the flight destined to ZZZ1 was diverting to ZZZ1; which was incorrect; but usually indicates something abnormal may be happening.Per 737 Flight Manual 'Landing at Nearest Suitable Airport' section; there are specific situations where pilot should plan to land at the nearest suitable airport to include 'Electrical - Only one AC power source remains.' No calls were made to the Maintenance Director or Chief Dispatcher until the diversion was in progress. Per the Dispatcher's Manual under the Dispatch Emergency/Irregular Checklist the Dispatcher should notify the Maintenance Director if the diversion to the nearest suitable airport is required. This also is in direct contravention to the Dispatcher's Manual for notification of any inflight notification of mechanical issues as well as the Dispatchers Manual Notification during irregular operations.The Flight Crew did [request priority handling] on arrival which was only discovered after I requested the Dispatcher get briefed by the flight. Failure to notify the Maintenance Director could have resulted in the [Company process] not being issued or company indication via Company process that [priority was requested] for a Operator flight.I have spoken with the Dispatcher for the flight to discuss the events in a post-review. After arrival in ZZZ the Director asked if I would issue the [Company Process]. I replied in the affirmative and requested the Director to have the Operations Managers advise the Maintenance Director when a similar significant event occurs. I was answered with silence.